Heart disease is a significant health problem which has been the subject of substantial medical study. Early treatments for angina pectoris, pain in the chest due to ischemia of the heart muscle, included, among others, attempts to revascularize the heart muscle by directly implanting vessels in the myocardium, by implanting tubes or vessels extending between the ventricle and the myocardium, and by performing acupuncture or channeling with a needle to carry blood from the ventricle into the myocardium. Acupuncture and channeling studies performed by P. K. Sen and P. Walter showed that the formed blood flow passageways and channels closed within a short period of time.
The Vineberg procedure, developed by Dr. Arthur Vineberg between 1930 and 1950, implanted the mammary artery into a tunnel created in an ischemic area of the myocardium of the left ventricle. Although the Vineberg procedure demonstrated successful animal trials which were supported by arteriograms from human subjects during the 1960's, the procedure remained controversial. Results of a 1972 randomized study conducted by the Veteran's Administration Hospital showed that just over 50% of the Vineberg grafts remained patent after one year. Dr. Vineberg reported higher patency rates in the results of a 20 year study in "Israel Journal of Medical Science", Vol. 11, No. 2-3, 1975, pgs. 250-263, which stated that implant patency was 80%, operative mortality was 2%, and anginal pain improved in 85% of cases. In the referenced article, Dr. Vineberg described the following surgical technique as necessary to achieve long term patency and collateralization with coronary arteries: careful preparation of the mammary artery with tying of the distal end and all but one or two of the intercostals; using forceps instead of a knife to tunnel at least 4 to 5 cm into an ischemic area of the myocardium located between branches of surface vessels in the apical, anterolateral or posterior arteriolar zones; and removal of the epicardium at the tunnel entrance.
The above treatments and associated research into Vineberg grafts and acupuncture techniques generally fell out of favor with the advent of coronary artery bypass grafts (CABG) which are vessel grafts attached proximally and distally around blockage sites in coronary arteries to "bypass" such blockages. Additionally, in the 1970's percutaneous transluminal coronary angioplasty (PTCA) procedures were introduced. Bypass surgery and PTCA have become commonplace; yet such procedures may not be able to revascularized all of the heart muscle, particularly the left ventricle of the heart, where blockages extend into the narrow distal portions of the coronary arteries.
Recent advances in cardiology have lead to improved bypass techniques and PTCA techniques (use of stents and atherectomy devices) thereby making it possible to attempt treatment of patients with severe coronary artery disease resulting in severely weakened, compromised hearts. Current statistics suggest that such patients present with less opportunity to achieve good CABG graft sites thereby resulting in estimates that 20-40% of CABG patents are not "fully" revascularized following CABG.
As the traditional treatments discussed above are expanded in use to attempt to assist severely weakened hearts, severely ischemic heart tissue is being treated and subjected to a sudden increase in blood flow. The flow/pressure differential which normally exists in the circulatory network supplying the heart muscle results from flow passing through vessels which progressively decrease in size as follows: the aorta, the coronary arteries, the arterioles, the capillaries, the veins, the coronary sinus, and finally into the heart chambers. Within this system, blood flows back and forth between capillaries and the myocardial sinusoids which receive blood from a constant exchange between sinusoidal vessels and the arterioles. In severely damaged heart tissue, this natural pressure differential is disrupted and may be unsuitable to accommodate the sudden introduction of relatively high pressure flow provided by a graft.
One alternative technique for treating areas untreatable with conventional CABG and PTCA procedures is known as transmyocardial revascularization (TMR). Procedures such as TMR, and drug therapy, enable treatment in areas that cannot be revascularized by CABG and PTCA. Although this technique was considered as early as the work of Dr. C. Beck "the Development of a New Blood Supply to the Heart By Operation", Annals of Surgery, Vol. 102, No. 5 (11/35) pp. 801-813, the method was not extensively studied until the work of Dr. M. Mirhoseini and M. Cayton, an example of which is found in "Lasers in Cardiothoracic Surgery in Lasers in General Surgery (Williams and Williams; 1989) pp. 216-223.
Clinical tests have demonstrated that TMR channels, which generally communicate with the ventricle, facilitate revascularization of the heart muscle and recovery of heart function. Recent studies further demonstrate that beneficial revascularization also occurs following creation of channels that do not remain patent and channels that do not communicate with the ventricular chamber. One mechanism for TMR revascularization is believed to be angiogenesis in response to injury created by the channel making device. Histology studies show the development of new vessels in the area of TMR channels. Dr. Vineberg reported in the article referenced above that new branches of implanted vessels occurred after a Vineberg procedure, and these branches joined with surrounding arterioles to revascularize the heart. Dr. Vineberg stated the collateralization to be caused by removal of the epicardium and lateral thrust because of the tied off distal end of the mammary artery. Angiogenesis research also is ongoing using agents such as growth factors and gene therapy products.
A laser device to perform TMR is described in Aita et al., U.S. Pat. No. 5,380,316, issued Jan. 10, 1995. In the procedure described in that patent, a number of channels are formed through the epicardium by means of a laser apparatus to extend through the myocardium to communicate with the ventricle. Other laser patents describing surgical transmyocardial revascularization include commonly owned U.S. Pat. Nos. 5,713,894; 5,738,680; 5,703,985; and 5,766,164.
A need exists for combined modalities of treatment to enhance revascularization treatments while taking into consideration the condition of the myocardium to be treated.
A need exists for apparatus and methods to evaluate the condition of heart muscle, particularly the blood flow in potential treatment sites, to optimize treatment results by, when necessary, altering existing pressure/flow conditions to accept direct vessel implants into myocardium.
A need exists for cardiac treatment procedures which include diagnostic tools to evaluate and select treatment sites and tools to enhance treatment success by preparing compromised tissue to accept and benefit from the sudden introduction of a new blood supply utilizing, where appropriate, combined treatment modalities such as direct vessel implants and TMR.
A need exists for apparatus and methods to modify a vessel to be implanted within myocardium to enable the vessel, particularly a vein, to resist the contraction forces of the heart to prevent occlusion of the implant.